The present disclosure relates to the manufacture and use of metal alloys, and in particular, to the use of metal alloys to infiltrate powder metal parts. Metal powder can be used to economically form a variety of complex-shaped metallic components or compacts by using a pressing and sintering process. Use of this method provides a powder metal part in near net shape, i.e., in the final desired size and shape, with minimal or no machining required. However, the resulting powder metal parts are loosely held together and exhibit relatively low impact and fatigue strength. These properties can be improved by infiltrating the parts with infiltrants that are typically copper based powders that may contain optional components such as, for example, lubricants and graphite. The infiltrant powder infiltrates the porous structure of the powder metal parts during the sintering process. The infiltrant powders are typically a mixture of copper and one or more additional metals.
The infiltration process for a copper-based infiltrant generally begins by placing the copper-based powder infiltrant in contact with the pressed and/or sintered powder metal part and subjecting this combination to a heating process which melts the copper-based powder. As the infiltrant powder melts, the molten material flows into the compact's pores. Components of the infiltrant can melt and diffuse into the compact at different rates. As a result, the distribution of copper throughout the infiltrated powder metal part can vary. Infiltrated articles having an uneven distribution of copper are more subject to rupture when subjected to a variety of forces.
Typically, a supplier or user of the infiltrant will press the infiltrant powder into a particular shape, such as a hollow cylinder, briquette, or pellet, to facilitate handling, shipping and/or storage, and to maximize its surface area that is in contact with the article being infiltrated. In these various forms the pressed infiltrant compacts can then be transported and utilized in a variety of infiltration processes. However, these pressed infiltrant compacts remain fragile and subject to breakage during their shipment and handling. This breakage increases waste and handling costs as well as environmental costs incurred to manage the resulting infiltrant particles or dust that can become suspended in the air and ultimately settle on work-surfaces. Workers must be protected from inhalation of this dust, so its removal from the workplace is necessary. Therefore, in light of the above, improved infiltrants and methods for their incorporation into powder metal parts are needed. Such improved infiltrants and methods for their use should avoid a majority of the disadvantages of the infiltrating powders described above. Particularly, such improved infiltrants should not be subject to breakage and powdering, should melt within a generally narrow temperature range, upon infiltration into a powder metal compact, provide generally uniform copper levels and impart strength to infiltrated article sufficient for its intended use. The present disclosure addresses these needs.